A rapid public health response was credited with keeping a “massive” anthrax
outbreak at a national park in Namibia from spilling over to infect humans or
livestock, according to a report published today in Emerging Infectious
Diseases.

“Human anthrax cases are known to be associated with outbreaks in animals,” Caitlin
M. Cossaboom, DVM, PhD, MPH, an Epidemic Intelligence
Service officer in the CDC’s Bacterial Special Pathogens Branch, told Infectious
Disease News. “In fact, contact with animals that have died from anthrax
is the most common route for humans to become infected with anthrax.”

No human cases

According to the report, between late September and early October 2017,
Namibia’s Ministry of Environment and Tourism (MET) identified a sudden die-off
of hippopotamuses and Cape buffalo in Bwabwata National Park. When the number
of carcasses topped 100, the MET notified the Ministry of Agriculture, Water,
and Forestry (MAWF) and the Ministry of Health and Social Services (MOHSS).

The CDC was consulted and assisted with the investigation, and a CDC field
team collected paired samples from seven animal carcasses. Using a novel assay
that can rapidly test samples in the field without refrigeration, Cossaboom and
colleagues came to a presumptive diagnosis of anthrax. Bacillus anthracis
infection was later confirmed by culture, real-time RT-PCR and
immunohistochemistry.

Interventions were initiated quickly. According to Cossaboom and colleagues,
the MOHSS developed and distributed a questionnaire to identify possible
exposures in people living near the park and found that 1,050 people reported
contact with or consuming meat from the carcasses. Each was given 2 weeks of
ciprofloxacin for postexposure prophylaxis and monitored for symptoms, they
said.

According to the report, the MOHSS also raised awareness of the ongoing
outbreak through education efforts and emphasized that people should not have
contact with or consume animals that are already dead.

No humans were infected, Cossaboom and colleagues reported. In contrast,
another team of researchers reported in 2017 that more than 500 people were
infected and five died in Zambia after being exposed to anthrax via the meat of
dead hippos.

“In this investigation, unlike previous outbreaks we have seen, 1,050 people
were quickly identified that had been exposed to anthrax, and thus had risk of
becoming sick,” Cossaboom said. “This highlights the importance of rapid
response to anthrax outbreaks in animals, including rapidly identifying people
who have been exposed and providing them with post-exposure prophylaxis, in
order to prevent humans from getting sick.”

Protecting livestock

According to Cossaboom and colleagues, livestock vaccination against anthrax
is required annually in Namibia to protect domestic animals and humans from
infection. To prevent spillover from the Namibia outbreak into susceptible
domestic animals, the MAWF secured approximately 10,000 doses anthrax vaccine
for a mass vaccination campaign.

Due to the size of the outbreak, field workers were unable to incinerate all
of the dead animals — the recommended disposal method of carcasses infected
with anthrax. Instead, they buried them at least 2 m underground to discourage
scavengers and then sprayed the burial sites with 10% formaldehyde.

No cases of anthrax in livestock were associated with the outbreak, and
wildlife deaths subsided by early December, Cossaboom and colleagues said. By
then, 155 hippos and 86 Cape buffalo had been disposed of, but Cossaboom and
colleagues noted that an earlier aerial survey of the park showed that 588
hippos and 2,216 Cape buffalo — around 26% and 4% of each population — had been
impacted by the outbreak.

“We want to highlight the importance of a rapid, multi-sectoral or One
Health approach when responding to anthrax outbreaks. Anthrax is endemic in
many countries throughout the world,” Cossaboom said. “Animals get infected and
die when they are exposed to anthrax in the environment. Human cases of anthrax
often occur associated with animal outbreaks, but fortunately in this case,
because of the rapid response by all partners, there were no cases of human
anthrax despite the massive outbreak in wildlife.”